let m be non zero Element of NAT ; :: thesis: for X being Subset of (REAL m)
for f being PartFunc of (REAL m),REAL
for i being Nat st X is open & 1 <= i & i <= m holds
( f is_partial_differentiable_on X,i iff ( X c= dom f & ( for x being Element of REAL m st x in X holds
f is_partial_differentiable_in x,i ) ) )
let X be Subset of (REAL m); :: thesis: for f being PartFunc of (REAL m),REAL
for i being Nat st X is open & 1 <= i & i <= m holds
( f is_partial_differentiable_on X,i iff ( X c= dom f & ( for x being Element of REAL m st x in X holds
f is_partial_differentiable_in x,i ) ) )
let f be PartFunc of (REAL m),REAL; :: thesis: for i being Nat st X is open & 1 <= i & i <= m holds
( f is_partial_differentiable_on X,i iff ( X c= dom f & ( for x being Element of REAL m st x in X holds
f is_partial_differentiable_in x,i ) ) )
let i be Nat; :: thesis: ( X is open & 1 <= i & i <= m implies ( f is_partial_differentiable_on X,i iff ( X c= dom f & ( for x being Element of REAL m st x in X holds
f is_partial_differentiable_in x,i ) ) ) )
assume that
A1: X is open and
A2: ( 1 <= i & i <= m ) ; :: thesis: ( f is_partial_differentiable_on X,i iff ( X c= dom f & ( for x being Element of REAL m st x in X holds
f is_partial_differentiable_in x,i ) ) )
thus ( f is_partial_differentiable_on X,i implies ( X c= dom f & ( for x being Element of REAL m st x in X holds
f is_partial_differentiable_in x,i ) ) ) :: thesis: ( X c= dom f & ( for x being Element of REAL m st x in X holds
f is_partial_differentiable_in x,i ) implies f is_partial_differentiable_on X,i )

proof

assume A3: f is_partial_differentiable_on X,i ; :: thesis: ( X c= dom f & ( for x being Element of REAL m st x in X holds
f is_partial_differentiable_in x,i ) )
hence A4: X c= dom f ; :: thesis: for x being Element of REAL m st x in X holds
f is_partial_differentiable_in x,i
let nx0 be Element of REAL m; :: thesis: ( nx0 in X implies f is_partial_differentiable_in nx0,i )
reconsider x0 = (proj (i,m)) . nx0 as Element of REAL ;
assume A5: nx0 in X ; :: thesis: f is_partial_differentiable_in nx0,i
then f | X is_partial_differentiable_in nx0,i by A3;
then consider N0 being Neighbourhood of x0 such that
A6: N0 c= dom ((f | X) * (reproj (i,nx0))) and
A7: ex L being LinearFunc ex R being RestFunc st
for x being Real st x in N0 holds
(((f | X) * (reproj (i,nx0))) . x) - (((f | X) * (reproj (i,nx0))) . x0) = (L . (x - x0)) + (R . (x - x0)) by FDIFF_1:def 4;
consider L being LinearFunc, R being RestFunc such that
A8: for x being Real st x in N0 holds
(((f | X) * (reproj (i,nx0))) . x) - (((f | X) * (reproj (i,nx0))) . x0) = (L . (x - x0)) + (R . (x - x0)) by A7;
consider N1 being Neighbourhood of x0 such that
A9: for x being Element of REAL st x in N1 holds
(reproj (i,nx0)) . x in X by A1, A2, A5, Lm2;

A10: now :: thesis: for x being Element of REAL st x in N1 holds
(reproj (i,nx0)) . x in dom (f | X)

let x be Element of REAL ; :: thesis: ( x in N1 implies (reproj (i,nx0)) . x in dom (f | X) )
assume x in N1 ; :: thesis: (reproj (i,nx0)) . x in dom (f | X)
then (reproj (i,nx0)) . x in X by A9;
then (reproj (i,nx0)) . x in (dom f) /\ X by A4, XBOOLE_0:def 4;
hence (reproj (i,nx0)) . x in dom (f | X) by RELAT_1:61; :: thesis: verum

end;

consider N being Neighbourhood of x0 such that
A11: ( N c= N0 & N c= N1 ) by RCOMP_1:17;
(f | X) * (reproj (i,nx0)) c= f * (reproj (i,nx0)) by RELAT_1:29, RELAT_1:59;
then dom ((f | X) * (reproj (i,nx0))) c= dom (f * (reproj (i,nx0))) by RELAT_1:11;
then A13: N c= dom (f * (reproj (i,nx0))) by A6, A11;

now :: thesis: for xx being Real st xx in N holds
((f * (reproj (i,nx0))) . xx) - ((f * (reproj (i,nx0))) . x0) = (L . (xx - x0)) + (R . (xx - x0))

let xx be Real; :: thesis: ( xx in N implies ((f * (reproj (i,nx0))) . xx) - ((f * (reproj (i,nx0))) . x0) = (L . (xx - x0)) + (R . (xx - x0)) )
reconsider x = xx as Element of REAL by XREAL_0:def 1;
assume A14: xx in N ; :: thesis: ((f * (reproj (i,nx0))) . xx) - ((f * (reproj (i,nx0))) . x0) = (L . (xx - x0)) + (R . (xx - x0))
then (reproj (i,nx0)) . x in dom (f | X) by A10, A11;
then A15: ( (reproj (i,nx0)) . x in dom f & (reproj (i,nx0)) . x in X ) by RELAT_1:57;
(reproj (i,nx0)) . x0 in dom (f | X) by A10, RCOMP_1:16;
then A16: ( (reproj (i,nx0)) . x0 in dom f & (reproj (i,nx0)) . x0 in X ) by RELAT_1:57;
A17: dom (reproj (i,nx0)) = REAL by FUNCT_2:def 1;
then A18: ((f | X) * (reproj (i,nx0))) . x = (f | X) . ((reproj (i,nx0)) . x) by FUNCT_1:13
.= f . ((reproj (i,nx0)) . x) by A15, FUNCT_1:49
.= (f * (reproj (i,nx0))) . x by A17, FUNCT_1:13 ;
((f | X) * (reproj (i,nx0))) . x0 = (f | X) . ((reproj (i,nx0)) . x0) by A17, FUNCT_1:13
.= f . ((reproj (i,nx0)) . x0) by A16, FUNCT_1:49
.= (f * (reproj (i,nx0))) . x0 by A17, FUNCT_1:13 ;
hence ((f * (reproj (i,nx0))) . xx) - ((f * (reproj (i,nx0))) . x0) = (L . (xx - x0)) + (R . (xx - x0)) by A8, A14, A11, A18; :: thesis: verum

end;

hence f is_partial_differentiable_in nx0,i by A13, FDIFF_1:def 4; :: thesis: verum

end;

assume that
A19: X c= dom f and
A20: for nx being Element of REAL m st nx in X holds
f is_partial_differentiable_in nx,i ; :: thesis: f is_partial_differentiable_on X,i
thus X c= dom f by A19; :: according to PDIFF_9:def 5 :: thesis: for x being Element of REAL m st x in X holds
f | X is_partial_differentiable_in x,i

now :: thesis: for nx0 being Element of REAL m st nx0 in X holds
f | X is_partial_differentiable_in nx0,i

let nx0 be Element of REAL m; :: thesis: ( nx0 in X implies f | X is_partial_differentiable_in nx0,i )
assume A21: nx0 in X ; :: thesis: f | X is_partial_differentiable_in nx0,i
then A22: f is_partial_differentiable_in nx0,i by A20;
reconsider x0 = (proj (i,m)) . nx0 as Element of REAL ;
consider N0 being Neighbourhood of x0 such that
N0 c= dom (f * (reproj (i,nx0))) and
A23: ex L being LinearFunc ex R being RestFunc st
for x being Real st x in N0 holds
((f * (reproj (i,nx0))) . x) - ((f * (reproj (i,nx0))) . x0) = (L . (x - x0)) + (R . (x - x0)) by FDIFF_1:def 4, A22;
consider N1 being Neighbourhood of x0 such that
A24: for x being Element of REAL st x in N1 holds
(reproj (i,nx0)) . x in X by A1, A2, A21, Lm2;

A25: now :: thesis: for x being Element of REAL st x in N1 holds
(reproj (i,nx0)) . x in dom (f | X)

let x be Element of REAL ; :: thesis: ( x in N1 implies (reproj (i,nx0)) . x in dom (f | X) )
assume x in N1 ; :: thesis: (reproj (i,nx0)) . x in dom (f | X)
then (reproj (i,nx0)) . x in X by A24;
then (reproj (i,nx0)) . x in (dom f) /\ X by A19, XBOOLE_0:def 4;
hence (reproj (i,nx0)) . x in dom (f | X) by RELAT_1:61; :: thesis: verum

end;

A26: N1 c= dom ((f | X) * (reproj (i,nx0)))

proof

let z be object ; :: according to TARSKI:def 3 :: thesis: ( not z in N1 or z in dom ((f | X) * (reproj (i,nx0))) )
assume A27: z in N1 ; :: thesis: z in dom ((f | X) * (reproj (i,nx0)))
then A28: z in REAL ;
reconsider x = z as Element of REAL by A27;
A29: (reproj (i,nx0)) . x in dom (f | X) by A27, A25;
z in dom (reproj (i,nx0)) by A28, FUNCT_2:def 1;
hence z in dom ((f | X) * (reproj (i,nx0))) by A29, FUNCT_1:11; :: thesis: verum

end;

consider N being Neighbourhood of x0 such that
A30: ( N c= N0 & N c= N1 ) by RCOMP_1:17;
A31: N c= dom ((f | X) * (reproj (i,nx0))) by A30, A26;
consider L being LinearFunc, R being RestFunc such that
A32: for x being Real st x in N0 holds
((f * (reproj (i,nx0))) . x) - ((f * (reproj (i,nx0))) . x0) = (L . (x - x0)) + (R . (x - x0)) by A23;

now :: thesis: for xx being Real st xx in N holds
(((f | X) * (reproj (i,nx0))) . xx) - (((f | X) * (reproj (i,nx0))) . x0) = (L . (xx - x0)) + (R . (xx - x0))

let xx be Real; :: thesis: ( xx in N implies (((f | X) * (reproj (i,nx0))) . xx) - (((f | X) * (reproj (i,nx0))) . x0) = (L . (xx - x0)) + (R . (xx - x0)) )
assume A33: xx in N ; :: thesis: (((f | X) * (reproj (i,nx0))) . xx) - (((f | X) * (reproj (i,nx0))) . x0) = (L . (xx - x0)) + (R . (xx - x0))
reconsider x = xx as Element of REAL by XREAL_0:def 1;
A34: dom (reproj (i,nx0)) = REAL by FUNCT_2:def 1;
(reproj (i,nx0)) . x in dom (f | X) by A25, A33, A30;
then A35: (reproj (i,nx0)) . x in (dom f) /\ X by RELAT_1:61;
(reproj (i,nx0)) . x0 in dom (f | X) by A25, RCOMP_1:16;
then A36: (reproj (i,nx0)) . x0 in (dom f) /\ X by RELAT_1:61;
A37: ((f | X) * (reproj (i,nx0))) . x = (f | X) . ((reproj (i,nx0)) /. x) by A34, FUNCT_1:13
.= f . ((reproj (i,nx0)) . x) by A35, FUNCT_1:48
.= (f * (reproj (i,nx0))) . x by A34, FUNCT_1:13 ;
((f | X) * (reproj (i,nx0))) . x0 = (f | X) . ((reproj (i,nx0)) . x0) by A34, FUNCT_1:13
.= f . ((reproj (i,nx0)) . x0) by A36, FUNCT_1:48
.= (f * (reproj (i,nx0))) . x0 by A34, FUNCT_1:13 ;
hence (((f | X) * (reproj (i,nx0))) . xx) - (((f | X) * (reproj (i,nx0))) . x0) = (L . (xx - x0)) + (R . (xx - x0)) by A37, A33, A32, A30; :: thesis: verum

end;

hence f | X is_partial_differentiable_in nx0,i by A31, FDIFF_1:def 4; :: thesis: verum

end;

hence for x being Element of REAL m st x in X holds
f | X is_partial_differentiable_in x,i ; :: thesis: verum